Reduction of metallic oxides



plll, 195l H. A. BRAssERr ET AL 295471,55

REDUCTION OF METALLIC OXIDES Filed Nov. 25, 1947 Patented Apr. 3, 1,951

2,547,685 REDUCTION oF METALLIC oXmEs Herman A. Brassert, Washington,Conn., and Fredrik W. de Jahn, New York, N. Y., assignors to H. A.Brassert & Company, New York, N. Y., a corporation of IllinoisApplication November 25, 1947, serial No. 788,084

(ol. vs -84)V 2 Claims.

iron and steel by direct reduction of iron oxides with a gaseousreductant comprising largely carbon monoxide, preferably admixed withhydrogen, and has particular reference to a method of controlling thecarbon content of the reduced v oxide while at the same time precludingsticking and fusing of the partially reduced oxide `and otherundesirableeiects during the reducing operation.

1t is Wellknown that iron oxides, such as hema tite, magnetite,limonite, roasted siderite, iron voxide derived from calcination offerrous sulphate, mill or roll scale, and the like, may be ,directlyreduced at temperatures below those at which their components soften orfuse, by means the hydrogen and carbon monoxide should bef substantiallyfree of hydrocarbons and the teln- `perature should be kept in thehigher ranges `for reduction according to this invention, because thecarbon deposition from carbon monoxide on reduced. iron only occurs atlower temperatures, i. e., about v700" C. and below. If

the melting stock high in carbon is desired, for instance, above 1%carbon, then a controlled 'amount of hydrocarbons can be added to thegas `mixture, andthe reduction temperature kept a's high asA possiblebutbelow the point of softening, vbecause the carbon deposition fromvhydrocarbons occurs at an increasing rate as the temperature increases,whereas carbon deposition from carbon monoxide occurs only in the lowertemperature range, as stated. As used herein, the

term carbon content in the product means the -total carbon, both thefree carbon and that combined as iron carbide or cementite, as in the'customary terminology of pig iron. f

Heretofcre, it has not been possible to contro the amount and rate ofcarbon deposition and as a result varying amounts of carbon were con.tained in the-reduced iron made by direct reduction with gasescontaining carbon monoxide or hydrocarbons, or both. When the desiredend Iproduct iste be pure powdered iron, such as is hrnostvcommonly usedat present .for the press- -This invention relates to the production ofing of nished parts, such as machine parts,

even a small carbon content may be objection? able. When the desired endproduct is melting stock for open hearths and electric furnaces in theproduction Vof steel, avarying carbon content is also objectionable asit makes it impossible to properly compose the charge and the variationthus intro-duced requires additional time while extra ore'or pig iron isadded to the heat to bring it to the desired composition.

In accordance with the present invention, methods are provided fordirectly reducing metallic oxides, particularly iron oxide, at reducingvtemperatures but without fusion and by means vof reducing gases,comprising largely carbon monoxide, preferably admixed withV hydrogen,under such conditions that the reduced end product has a controlledcarbon content .varying from zero to any desired'percenta'ge up to 3%,or more. Under these conditions a melting stock may be made with theparticular car'- bon content most suitable for the optimum technical andeconomic operation of open hearths and electric furnaces in any plantunder existing local conditions, and the carbon content mayV be variedat will to suit any change in local conditions. For example, ifv thegrades of steel produced, `4and other considerations, require an open.,hearth charge consisting of steel scrap containing .15% carbon and 20%pig iron containing 4% carbon, the composite carbon content Vof thecharge can be reproduced by using approximately only 60% steel scrapwith Ll0% of the melting stock made according to this invention, with acarbon content of 2%, or by ,using solelyfa VT% melting stock chargecontaining .90% carbon' made according tov-this vin.- .Vent0n Y,

The invention -is preferably carried out -by the use of a highpercentage of carbon monoxide, for instance '70% to 80% carbon monoxideand 20% to 30% hydrogen, although different .proportions of carbonmonoxide may be em'- ployed. However, where the charge comprises nodulesofthe iron oxide, as is preferred, the use of carbon monoxide by itselfhas the objection that it causes the charge to swell and the nodulesbecome highly friable. Moreover,

lpure carbon monoxide is diii'icult and expensive to produce, andmixtures of carbon monoxide and hydrogen as mentioned representthecheap*- est form of reducing gas suitable for this process which can beproduced, and the presence of the hydrogen appears to eliminate swellingand disintegration of the iron oxide charge, which makes `furnaces.

'the temperature is of prime importance. -temperature control accordingto the invention the reducing operation diicult. Such mixtures of carbonmonoxide and hydrogen can be made from any solid fuel, such as coal andcoke, anthracite, lignite, peat char, charcoal, and the like. By the useof oxygen and steam, the production of such gas mixtures can becontinuous, and in many cases more economical than when air and steamalternately are used, as in standard water gas practice for thegasification of The water vapor can be added to the gas mix-- ture bybringing it in contact with water of the proper controlled temperatureor by addinga measured amount of steam, preferably under automaticcontrol. In this way, the carbon content in reduced iron can be held toas low as .1% and less, thus bringing it in line in respect to carboncontent with the lowest carbon scrap ,obtainable for open hearth andelectric furnace charging. On the other hand, carbon can be added to theiron by this method, so as to make the melting stock the equivalent ofmixtures of steel scrap and pig iron, thereby replacing pig iron :forthat purpose.

Complete deoxidation of the iron oxide, such :as may be required foriron powder, is generally not desirable for melting stock since thesmall amount of oxygen left in the melting stock improves its meltingquality and accelerates the making of steel in op-en hearths andelectric If complete removal of oxygen is required, together withabsence of carbon, as for instance in the production of pure iron forthe A powdered metal industry, this result can be obtained by theadmission of pure hydrogen and a small amount of water vapor in thefinal stage of reduction. The pure hydrogen will complete the reductionand the water vapor will eliminate f any carbon present. It may also bedesirable to produce a completely reduced powder substantially free fromoxygen but containing a certain controlled amount of carbon, whichpowder then would be equivalent to a steel powder and could be used forpressing steel parts or billets, slabs vand sheet bar for subsequentrolling, forging or extruding, thus entirely circumventing the of thegas and more water vapor is required per cubic foot of gas with the risein temperature to produce the same carbon removal, the control of Thisthe baked nodules entering the reducing Zone from the baking zone abo-e.

For a better understanding of the present in 'vention, reference may behad to the accompany- 'i'ng drawing, which comprises a typical flowsheet illustrating the procedural steps of the process 'according to thepresent invention.

If the iron oxide to be reduced is in the form of nodules, pellets orglomerules,` produced acvvcording to Dean Patent No. 2,131,006, then weprefer to discharge such nodules while still hot from the baking processdirectly by gravity into the reducing zone through suitable gas seals toseparate the oxidizing baking zone I0 from the reducing zone Il. Ifiinely divided iron oxide is to be reduced directly without priornodulizing and baking, then the reduction may be carried out byfluidization, as, for instance, according to the invention disclosed inPatents Nos. 2` 316,69@ and 2,389,133. issued jointly to applicant H. A.Brassert and others.

In carrying out the invention, the reducing operation is conducted inthe presence of a mixture of carbon monoxide and hydrogen, and usuallycontaining some nitrogen. The ratio of carbon monoxide to hydrogen isabout one part of hydrogen to about three to four parts of carbonmonoxide. Preferably, the gas contains from three and one-half to fourtimes as much carbon monoxide as hydrogen, by volume, although anincrease in hydrogen and a decrease in the carbon monoxide within therange specified does not produce appreciably different results inrespect to the reduction of the oxides or the removal of oxygen. Themixture of gases may be generated either in a gas generator I2 similarto a water gas generator which may be fed with coke or coal. Steam andair or oxygen are blown through the glowing bed of coke, coal, or othercarbonaceous matter to generate the gas.

If desired, the gas mixture may be made by reforming hydrocarbons, suchas products from natural gas or renery gases or hydrocarbons up to andincl"ding C4 hydrocarbons in the generator I3. The gas generated ineither the generators I2 or I3 is delivered to a carbon dioxide absorberIt which may contain methanolamine solfiion (M. E. A) for absorbing thecarbon dioxide from the gas. The gas passing from the absorber consistsessentially of hydrogen, carbon monoxide, nitrogen, and a relativelysmall amount of carbon dioxide. The gas is delivered to a steam drivencompressor I5 which in turn supplies the gas to a heat exchanger I8where the gases are heated before delivery into the reducing furnace II. The partially heated reducing gas passing from the exchanger I6 ishumidied at 26 by addition of water vapor in the form of steam and ispassed through a gas heater I1 which raises the gas temperature to thatrequired to maintain the temperature in the reduction zone in furnace II between about '750 C. and about 900 C. Thus, if the nodules enter thefurnace I I at 850 C. from the baking furnace I0, and it is desired toreduce they nodules at 850 C., the gas entering the furnace II needsupply only sufficient additional heat to com.- pensate for that lost inthe endothermic reducing reaction.

The spent gas from the furnace II, now consisting principally ofhydrogen, carbon monoxide,

steam, carbon dioxide and nitrogen, may be passed to the heat exchangerI6 to heat the incoming reducing gas and may be discharged to a gaswasher and condenser I8 which is cooled by water. A part of the washedspent gas may be bled off through the valve I9 and returned to theheater Il for combustion therein to heat the reducing gas supplied tothe furnace. Another part of the spent gases from the Washer I8 may bemixed with freshly generated gas from the generators I2 and I3 andreturned therewith to the absorber I4. f

The carbon dioxide absorbed in the absorber 'I4 may be recovered andreduced in either of the vgenerators I2 and I3, by delivering thelmethanolamine solution to a reboiler 2li-heated by Waste'steam fromcompressor I5 and a waste 'heat boiler which is heated bythe combustion`gases from the heater I l.. The carbon dioxide is driven olf in thevreinoiler and the methanolamine is cooled in the cooler 2| and returnedto the absorber I4 for use therein.

' `Only about half of the carbon dioxide from the reboiler 20 iis usedin the generator I2, inasmuch as two volumes of carbon monoxide areproduced from one volume of carbon dioxide therein, the remainder beingbled off to atmosphere through the valve 22. All of the carbon dioxidemay be supplied to the generator I3 for in this apparatus one volume ofcarbon monoxide is produced for each volume of carbon dioxide suppliedthereto. The valves 23 and 24 are utilized to control the supply ofcarbon dioxide to the gas generators I2 and I3.

We have found that a substantially dry reducing gas consisting of aboutequal parts of vcar-- bon monoxide and hydrogen, containing less than:002 pound of Water vapor per cubic foot and being free fromhydrocarbons, will give a reduced -1 about C. and about 70 C.,'Vand thenutilizing 'a given reduction temperature within a comparatively narrowrange, a verymarked change in the carbon content of the reduced materialcan be obtained. For instance, nodules'made from New Jersey magnetiteconcentrate and containing i about 72% Fe and .2% SiOz were reduced withwater vgas containing 46% CO and 50% hydrogen, the gas beingsubstantially dry, containing less than .0005 pound Water vapor percubic foot.

ita temperature in the reduction zone of 850 C; the product contained.44% carbon. Repeat- We have also z;

.6 tent" greater than 1% is desired, say up to 2%"or more, a suitablehydrocarbon, such as methane, propane, or the like, may be added at 3|,and the volume thereof controlled by valve 32, either manually orautomatically, to control the carbon content of the reducing gas. B ythuscontrolling the carbon content of the reduced oxides, melting stockhaving virtually any desirable characteristics may be provided for themanuafacture of iron and steel products.

If the reduced material is discharged from the reducing `furnaceinrelatively finely-divided form, whether partially ,or more completelyre' duced, it may be briquetted under a reducing atmosphere and whilestill hot, with or without admixture of alloying metals, as described inPatent No. 2,287,663, issued June 23, 1942, to applicant Brassert. Also,if theoutput of reducing furnace II is reduced nodules, they may besimilarly treated to provide the desired melting stock formula.

In a typical operation involving charging the reduction furnace at therate of 100 pounds iron oxide nodules per hour, gas from a standardWater gas set containing 30 per cent carbon monoxide, per cent hydrogen,2 per cent carbon dioxide and 23 per cent nitrogen Was used and was thensaturated with Water `vapor at from 40 to 42 C., making a water vaporcontent of .0035 pound per cubic foot. No hydrocarbons were present. Onleaving the reduction furnace, the oil gas contained 21 per cent carbonmonoxide, 39 per cent hydrogen, 15.4 per cent carbon dioxide, and 24.6

, the utilization of the hydrogen in the gas. This is quite differentfrom when dry gas is used.

than the utilization of carbon monoxide.

ing the reduction in exactlythe same way, with F the same gas flow, samewater gas analysis, same A,temperature and the same iron oxide, butsaturating the gas with water vapor at about 50 C. equivalent to about.006 pound of water-vapor per cubic foot. the carbon content of theproduct was reduced to .06%.

In some cases, for example, when the product is melting stock to be usedas a substitute for steel scrap or pig iron in the smelting operation ofopen hearth and electric furnaces, a denite amount of carbon is highlydesirable. By automatically regulating the water vapor content of thergas and the temperature in the reducing furnace, it is possible toprovide the desired and necessary carbon content in the furnace charge.Water regulation is preferably automatic and may be eifected by aconventional automatic flow control apparatus 25 Iin steam supply pipe23 and responsive to the water vapor content in the reducing gas mixtureas supplied to the furnace II. Similarly, the temperature in reducingfurnace II may be accurately regulated by controlling the supply offuellby a valve 21 in the combustion fuel line 28 responsive to theaverage temperature in the gas heater I'I as determined by pyrometers orthermostats 29 and 30 therein. e

When a melting stock having a. carbon con- Then, the utilization ofthehydrogen is higher The resulting product with a total Weight of 3500pounds contained an average of .17% carbon.

The best results were obtained at temperatures as near 900 C. aspossible. Temperatures between about 825 and 875 are preferable for thereason that the rate of reduction at these temperatures is high, andfusing or sticking of the nodules is largely eliminated. Moreover, thesteel alloys used in the reduction chamberare notrsoftened or weakenedat temperatures oi' this order, and there' is no substantial swellingAof the nodules, as may occur at higher temperatures. K

The advantages of the use of water vapor in the reducing gas are bestshown by the following tests: K

A dry gas consisting of 60 per cent hydrogen and 40 per cent carbonmonoxide was used to reduce nodules of iron oxide at a temperature of800 C. The resulting product contained 1.96 per cent carbon andreduction was only per cent complete.

Similar tests were conducted with reducing gas which had been bubbledthrough water at 30 C. and then used for reducing nodules of the sameiron oxide at 800 C.

The compositions of the reducing gases were:

The following deoxidations and carbon contents: were obtained.'

D.c.0xi :Carbon cation Gon tent Per cent Per cent l 94. 3 .135

advantage of reducing the heat needed for the reduction. This isexplained by the fact that the heat needed when using pure hydrogen isapproximately 814,000. B. t. u. per ton of iron and` that the heatgenerated when using. carbon monoxide is approximately 140,000 B. t. u.per ton ofy iron.

From the preceding description, it will be apparent that the use ofcontrolled amountsv of water vapor in mixtures. consisting principallyof hydrogen and, carbon monoxide greatly benefits the reducing operationand results in a more completely reduced and purer form of product. Thisproduct is suitable for use to repace scrap iron or steel, and, if it isdesired to produce powdered iron therefrom, it can be treatedeiiiciently with hydrogen to complete the reduction of the smallpercentage of oxide remaining therein. It will bev understood that theproportions of the carbonnionoxide and hydrogen may be varied suitablyand that these gases can be obtained from any available source.Therefore, the embodiment. of the invention described herein should beconsidered as illustrative and not as limiting the scope of thefollowing claims.

We claim:

l. A method of reducing iron oxides which comprises bringing iron oxideheated to between about 750 C. and about 900 C. into Contact with aheated reducing gas consisting essentially of carbon monoxide andhydrogen in the ratio of about three to about four parts by volume ofcarbon monoxide to each part of hydrogen by volume, introducing watervapor into said gas to maintain the water content of the gas within arangev between about .002 and about .01 pound of water vapor per'cubicfoot of gas and in.- creasing the water vapor content, within saidrange, to decrease the carbon content of thereduced oxide, anddecreasing the water vapor content, withinv said range, to increase thecarbon content of said reduced oxide.

2. A method of reducing iron oxide, which comprises treating the oxidein a reducing zone at between about 750 C. and about 900 C. with areducing gas consisting essentially of hydrogen and a carbon-containinggas, said carbon-containing gas. being capable of being cracked at saidtemperatures in the presence of said iron oxide to depositV carbonthereon, saidcarboncontaining gas being present.v in a ratio of. about2A; part to 4 parts by volume. to one part of hydrogen, introducingwater vapor into said reducing gas to maintain awater vapor content inthe gas Within a range between about .002 and about .01 pound of watervapor per cubic foot of gas, said water vapor content being increased,Within saidy range, to reduce the carbon content of the reduced oxideand decreased, Within said range, to increase the carbon content of thereduced oxide.

HERMAN A. BRASSERT.v FREDRIK W. DEv JAHN.

REFERENCES CITED The following references are of record' inthe file ofthis patent:

UNITED STATES PATENTS' Number Name Date 1,256,623 Westberg et al. Feb.19, 1918v 1,310,724 Westberg July 22, 1919 1,758,786V Ekelund May 13,1930 2,048,112 Gahl July 21,y 1936 2,131,006 Dean Sept. 30, 19382,166,207 Clark July 1,8, 1939 2,287,651 Turin June 23, 1942 2,368,489Patterson Jan. 30, 1945 2,329,862 Terry et a1 Sept. 21, 1943 OTHERREFERENCES Sponge Iron Low in Impurities by Ekelundrs Process, MetalProgressl v01. 20 No. 4, October 1931, pages 89 and 90.

Pilot-Plant Investigations, Production of Sponge Iron, U. S. Bureau ofMines Report of Investigations 3994 (December 1946).

Controlled Atmospheres for the Heat Treatment of Metals by Ivor Jenkins,published 1946, pages 212, 213 and 280-285.

1. A METHOD OF REDUCING IRON OXIDES WHICH COMPRISES BRINGING IRON HEATEDTO BETWEEN ABOUT 750* C. AND ABOUT 900* C. INTO CONTACT WITH A HEATEDREDUCING GAS CONSISTING ESSENTIALLY OF CARBON MONOXIDE AND HYDROGEN INTHE RATIO OF ABOUT THREE TO ABOUT FOUR PARTS BY VOLUME OF CARBONMONOXIDE TO EACH PART OF HYDROGEN BY VOLUME, INTRODUCING WATER VAPOR ITOSAID GAS TO MAINTAIN THE WATER CONTENT TO THE GAS WITHIN A RANGE BETWEENABOUT .002 AND ABOUT .01 POUND OF WATER VAPOR PER CUBIC FOOT OF GAS ANDINCREASING THE WATER VAPOR CONTENT, WITHIN SAID RANGE TO DECREASE THECARBON CONTENT OF THE REDUCED OXIDE, AND DECREASING THE WATER VAPORCONTENT, WITHIN SAID RANGE, TO INCREASE THE CARBON CONTENT OF THEREDUCED OXIDE.